Spectroscope grating having spaced zones of diffraction lines



March 1949.

- F. J. KAEHNI El AL sPEcTRoscoPE -GRATING HAVING SPAGED ZONES OFDIFFRACTION LINES s sheets-#sheet 2j Filed Feb. 16'. 1943v FIEL? FI E. E

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March 1, 1949. F.' J. KAEHNI ETAL 2,463,280

SPECTROSCOPE GRATING HAVING SPACED ZONES OF DIFFRACTION LINES FilledFeb. 16,1945 s sheets-sheet s nl l '22 F1517' 20d 27 26 42 gnll d @6 M4n JU. 26 J2 1 l z2 l 3 l l a l J L. A 'jj' l l NVENTOR -A BY Z/rLLLf/MZ/fffEH/nrf Patented Mar. 1, 1949 SPECTROSCOPE GRATING HAVING SPACEDZONES OF DIFFRACTION LINES Frank J. Kaehni and William L. Kaehni,Cleveland, Ohio Application February 16, 1943, Serial No. 476,082

4 Claims.

This invention relates to a new form of spectrum gratings commonlycalled diffraction gratings, and the essential objects include producingsuch a grating upon surfaces .of transparent bodies. An advantage of ourinvention is its adaptability for use on plain or plate glass withoutthe necessity of tedious time-consuming preparatory grinding operations.An object is to provide a method for so treating such surfaces as toproduce thereon a minutely, nely, even spaced series of lines of uniformcharacter, with comparative cheapness and within a remarkably shorttime.

More specilc objects are to trace essentially circular gratings, formingsuch lines in almost perfect circular bands .or AZones with uniformityand accuracy and by the most simple method, and of any desired spacingfrom a few say, 100 to an inch up to as many as is practicable for theintended use. It is entirely possible to make, and in fact we have made,gratings by our method with line divisions ranging from 20,000 to40,000, or even more, uniformly spaced lines per inch.

A more specific object is to provide a method or means for tracing suchlines by a relatively rotary motion between the tracing stylus formingthe diffusion and diffraction edges or opaque lines, and the surfaceupon which the line is being traced, while advancing the stylus relativeto each preceding line and in one continuous operation for any givendiffraction band or zone. An important characteristic of the process isthe maintaining of the line forming point in constant contact, avoidinglifting of it, intermittent on opposite sides of a transparent body suchas a plate or block of glass.

In addition to simplicity, cheapness of manufacture and ease ofobtaining unusual accuracy in the making of diffraction gratings, whichwill meet the requirements of a wide variety of oommercial laboratoryand scientific uses, this cir-' cular band arrangement opens new fieldsof uses of accurate grating spectroscopes, as well as lending accuracyto cheaper, more quickly produced forms ordinarily chosen for widespreadeveryday uses.

Some of the examples of useful applications of our invention includenight-sights; use in optical instruments in place of or in combinationwith cross-hairs; eye testing instruments for comparison of the two eyesfor the differences in color response; and range finders and directioninstruments of remarkable accuracy; blackout warning signals having adefinite operational effect giving distance by color readings; asindicators of direction and color of a source of light.

Aside from the foregoing uses, innumerable decorative effects on flatglass Wear, hollow glass and opaque table Ware, mirrors, and numerousother uses may be effected. The tracingV of the spacing movements andother troublesome steps in previous processes.

Other objects include the mounting of a stylus such as a diamond pointso that it may firmly hold against movement which would permit variationof line spacing and yet which permits a resilient, almost perfectlyuniform contact pressure against varying surfaces or undulations, suchas occur on common glass or commercial plate glass.

Still other objects are to provide series of concentric circular zonesof continuous spiral diffraction lines on the same surface and the linesof each zone being of predetermined spacing having such relationships tothe neighboring zone, as may be desired for many purposes, some of whichare hereinafter mentioned.

Still another object is to provide diffraction gratings in substantiallycircular co-axial bands spirals on a common axis may be modified byadvancing the circular movement of the stylus acrossvthe surface beingtreated and modifications of the circular movement into angular, polygonor fanciful designs have been found to give rainbow effects of a varietyof patterns in striking beauty.

Reproductions upon plastics may be made by dies formed by the samemethod, then with the die gratings so formed on them they are used toimpress the lines on the surface of the plastic transparent bodies.

The foregoing various other objects will become apparent in thefollowing specifications and we desire that it be understood that theuses herein mentioned are indeed but a few of the possibilities for bothscientific and pleasure giving purposes for which our invention may beadapted.

A number of embodiments of our invention are described in connectionwith the accompanying drawings in which are indicated various types ofdiffraction grating formations and groupings.

In the drawings we also show an illustrative form of mechanism forcarrying out our process.

Fig. 1 is a face view of a transparent plate bearing grating linesformed according to 4our invention.

2,4ce,aso

Fig. 2 is a transverse section of same.'

Fig. 3 is a face view of a similar transparent plate having a wide zoneof grating lines.

Fig'. 4 is a similar plate showing the grating lines formed intoseparated zones.

vFig. 5 is a section through a'gratlng such as Fig. 3, showing lightlines from a source through the grating, to the eye.

Fig. 6 is a modified form showing a narrow band of grating lines on acircular transparent plate with an opaque center piece.

Fig. 7 is a transverse section through the same.

Figs. 8 and 9 are face and section views showing an arrangement of threenarrow zones of grating lines.

Figs. 10, 11 and 12 are sectional views showing in greatly enlargedscale in conventional form the approximate nature of the opaque ordiffusion lines formed on or in the plate surfaces.

Fig. 13 is a diagrammatic sectional view showing two grating platesmounted in a sight tube with a lens and illustrating passage of lightfrom a source of light to the eye.

Fig. 14 is a similar view showing a grating such as Fig. 6 mounted in adifferent form of tube.

Fig. 15 is a sectional view showing gratings on opposite faces of thetransparent block.

Fig 16 illustrates a disc-like grating in half circular form with aspectrum band thereon showing diffraction sighting.

Fig. 17 is a conventional plan view illustrating a mechanism for formingthe grating lines.

Referring for convenience toFigs. 1, 2 and 17 we will rst describe ourpreferred method of forming the spaced diffraction lines upon a planesurface. A block I, shown as rectangular, having been cut from suitableplate glass, with both surfaces of the usual approximate accuracy andwithout preliminary grinding treatment, is selected of a size suitablefor the contemplated use of the intended grating. A thickness such asshown in Fig. 5 is suitable for many purposes,

although as shown in Fig. 2, for other uses greater thickness ispreferred.

The plate or block I is first mounted against the flat surface of theface-plate carrier I2 and held rmly as by spring clamps I4. The faceplate is preferably rigid with a shaft I5 mounted in bearings I6 and I1and arranged to be driven at a uniform speed by any suitable drivingmechanism. 'Keyed to the shaft I5 is shown a gear 20 meshing with apinion 22 on a shaft 25, mounted in bearings conventionally indicated at2B and 21, and driving screw or worm 28 in turn meshing with its wormgear 30 on a shaft 32.

The shaft 32 is provided with a screw worm 35 driving the worm gear 36to rotate a master feed screw 40 to which it is firmly fixed. The feedscrew 40 is preferably provided with accurately tted bearings 42 and 44,the latter being provided with a thrust bearing collar 45, fixed on thescrew shaft and at the outer side of the bearing may be provided amicrometer-like adjustment indicated at 48 which may be operated totighten the screw by knurled nut 49. As shown, v

beneath the feed or lead screw 40 is provided a cross slide 50 having acommon form of dove-tail guide 52 rising therefrom andengaging a guidingtool carrier slide 54, having a master feed nut engagement withthe screwas indicated at 56.

Transversely slidabie on the carrier 54 is tool carrier proper, 60,having a manually operated micrometer adjustment designated 62. Suitablymounted on the tool carrier as br.' screws 63 is a tool holder 65, inturn carrying a resilient cutthat at which it may heat to any suchdegree as,

ting tool arm 68 having at its free end a marking or cutting part suchas a diamond point indicated at 10.

In operation the spacing of the grating lines having been predetermined,the ratio of the gears as at 20 and 22 having been selected as thoseshown in solid lines, the alternate gearing, comprising different sizesof gears and pinions as in a change-speed back gears being indicated at23 and 24, it will be seen that as the work piece or grating plate I isrotated'wlth the carrier face plate that the worm and gear transmission28 and 30 and 35 and 36 will rotate'the master feed screw 40 relativelyslowly, that is, perhaps one revolution of the screw for each or 200revolutions of the work plate. thus the tracing point moving radially ofthe carrier axis, spiral lines such as indicated at 2 and 3 on a platein Fig. l with a spacing of 2,000 to 4,000 per inch will be formed.

As a specific example, if it be desired to make grating lines on theplate surface spaced 2,500 lines per inch, assuming that the lead screw40 had 20 threads per inch and is rotated by the first worm and gearcouple at 20 to 1 ratio and by the second worm and gear couple at 25 to1 ratio and the ratio between the plnion'and gear 22 and 2J is 1 to 4,we have 20 X 20 25, i. e. 10,000 divided by 4-the worm and pinion ratioresulting in 2,500 revolutions of the work piece for 1 Inch advance ofthe diamond point. If the ratio of the back gears between the shafts I5and 25 be approximately 1 to 1, and the two worm and gear Icouples areeach 100 to 1, the threads on the lead screw 40 at 20 per inch will givey20,000 lines and at 40 per inch, pitch of the lead screw will give40,000 lines cut'or traced spirally on the surface as indicated at 1, 2and 3 for each inch width measured on the radius from the axis of theplate. Y

The resilient arm 68 is preferably wider tha its thickness to resistlateral movement, but its thinness permits considerable resilient actionor movement of the diamond point over any undulations which may bepresent on the plate surface without altering the pressure upon thediamond cutting stylus. Thus the depth of the cut in the surface is notlarge and yet the relative position of the cutter may be accuratelymaintained and a smoothness and regularity of the resultant gratinglikewise is accomplished, even though the surface vhas not been preparedby processes such as optical grinding.

The comparative accuracy of width and depth of `grating line withoutchange in its uniformity, is likewise much more readily attained. thanwere the tool Jto be lifted and caused to re-engage the work as has beenthe practice in parallel line gratings. This comparision is* madebecause the speed with which reciprocating motion cutting has been donein the past is extremely slow. In contrast, we have cut spiral linessuch as indicated in zones 1 to 2 inches wide as appears at 4 in Fig. 3and on separated zones as at 6 and 1 in Fig. 4, in but a few minutes toan hour, depending @upon various conditions and essentially upon therequired number of lines per Inch.

The cutting or tracing speed of the diamond point or stylus on thesurface is maintained below will affect the surface or point. Alsocomparatively low speeds are used to avoid relative vibration, however,it will be seen that 3,600 lines may be traced on a band or zone 1 inchwide, measured radially at the rate of one revolution per second. Thatis, within one hour i. e. 3,600 seconds, the cutting tool would moveacross the surface l inch radially traveling, producing in effect 2inches of grating on the diameter. If the outer circle is relativelysmall, speeds of several revolutions per second may be used, thus withinpracticable limits forming one to several inches of grating zone in amatter of minutes or part of an hour. Likewise, by rotating the workpiece at one or two hundred revolutions per minute good results ingrating line spacings from 8,000 to 15,000 or even 20,000 lines per inchmay be attained, and such grating still requires only an hour or two,depending somewhat upon its size and the hardness of the surface beingworked upon.

Fig. 5 illustrates a simple use of a single zone `diffraction gratingand in this view a diffraction zone 4 corresponds to the arrangementshown in Fig. 3. Light passing from a source indicated at 8 as by lines9 leads to the eye at the left. When the center line or normal axis ofthe grating is slightly out of line, as for example, as when passingthrough a point indicated by a cross or X in Fig. 3, the spectrum orspectra, as there may be several, depending on the distance between thegrating and the eye and the source of light, will be seen' in narrowradial zones designated 5 in Fig. 3 and shown by the heavier lines inthe grating. The narrow spectral radial zone will appear very much asthe heavy shaded portion. This' serves as a guide line along which thegrating or eye may relatively move to bring the source light through thecenter of the circular diffraction zone, at which time the spectrum willappear entirely around the circle. 'I'his circular spectrum is notattempted to be shown in the line drawings but with any arrangement oflines of suitable spacings in a zone such as shown in Fig, 3, primaryand secondary, and even third and fourth spectrum may be seen, and eachin full circular form.

The angle Y in Fig. 5-for the outer light line 9 is the same for a givencolor as is this angle measured in the same way as a light beam passingthrough parallel gratings. The advantage is, however, that instead ofthe grating being in a comparatively narrow band from a small slit forthe light source, a pin hole opening or distant single light shows theentire spectrum in a circular band. In using gratings with straightparallel bands, the light source is usually arranged to show in a narrowline or extremely narrow slit through which the light passes andsuitable readings may be taken only when the lines are parallel with theband of slit at the light source. In contrast a point light ordistantsource or even a larger circular light may afford effects withour gratings, not possible with the parallel straight line grating.

We have not found in the prior art a mathematical expression forcomputing the angle for given colors at certain angular relationships.However, we have discovered that the angle Y, Fig. 5, has a simplerelationship to the rst order spectrum. Assuming 8Z as light raysarriving parallel to the axis and normal to the plane of the grating:

Then the diffraction angle or angle of bending due to light diffractionarriving at the eye for any particular color or wave length may beexpressed by the formulawhere 1 is tne wave length of the particularcolor; d is the grating spacing or distance between adjacent lines ofgrating and X is the angle as shown.

The spaced zones of Fig. 4 may ,correspond to the width of a given coloror to several colors of the spectra and each producing its own spectra.The spectra will appear in uniform circles in any pair of zones orwithin the broad Zone of Fig. 3 very much as the zones 6 and 1 of Fig.4. If two such plates or discs with the zones like Fig. 3 are spacedapart in true alignment and brought into axial alignment with the lightsource or target, before the full spectrum appears, visibility throughthe plate is only slightly less than through a cl'ear glass with crosshair line arrangement as the center lines are there shown. Obviously,very quick and accurate sighting may be made because the target isvisible and it may be brought down the narrow band or beam of thespectrum from either sight to the center as described in connection withthe band 5 in Fig. 3, and one, two, or more zones of complete spectraappear, as in Fig. 4, the plane of the grating will be controllednormally to the line of sight t0- ward the source of light. For certainpurposes an opaque center may be formed and it is found useful for anarrow band of wave lengths formed by a narrow band grating, as at 4a inFig. 6, the opaque center being formed of any suitable material asopaque cutting or a disc as indicated at small d, Figs. 6 and 7. Severalbands, suchas 4b, 4c and 4e in Figs. 8 and 9,*may be used for variouseffects, for example, by properly spacing the lines for each bandaccording to the above formula, the same color, for example, red, can beobtained over the entire field of each narrow band at a predetermineddistance from the light source 8.

Incidentally, this produces very striking ornamental effects when thegrating is viewed at different angles with relation to point source oflight.

In tracing the lines on ordinary plate glass, we have found that diamondpoint producing diffraction lines indicated conventionally in very muchlarger scale in Figs. 10, 11 and 12, as indicated by L, L and L", areformed about as follows: A spring tension holder, or a spring armsupport, indicated at 68 in Fig. 17, carrying a diamond point 10, isbrought into contact with the glassA surface and a movement of a fewthousandths of an inch of the carrierl toward the glass to give a slightfraction of an ounce of pressure will produce lines of the approximatecontours shown in Figs. l0, 11 and 12, and evenly spaced. The springtension does not cause the diamond to penetrate more than the distanceof .005 of an inch but it will apparently press into the glass withoutcutting action, deforming the surface in a line appearing perhaps,one-ten/thousandth of an inch deep, more or less.

Minute irregularities of the diamond point apparently do not adverselyaffect results. A scratchy diamond point will produce lines attempted tobe illustrated in cross section at Fig. 12. Diffusion or diffractioneffect, however, is such that light rays passing through are distortedby the cut portion of the grating surface thereon, and such lines passaway from the eyes or the eye-piece, leaving the true diffraction effectof the undistorted surface of the eld functioning, so far as visibilityand photographic purposes are concerned, about as effectively as thoughthe grating were formed by alternate transparent and opaque lines.

In Fig. 13 the grating members f and y are manso shown as mounted in atube T with the grating bands lh and 4k respectively at slightlydifferent zones and the eye-piece E may comprise a suitable lens for thepurpose desired.

Fig. 14 shows mounting of a grating plate or disc such as shown in Fig.6, with the opaquecenter disc d and single grating band 4a. Here theends of the telescoping tube formed of two parts, Tl and T2, willproduce concentric rings of color or light emitting from the eye-piecehole H, where light is admitted through a small hole HI from the lightsource as shown at C. By graduated lines indicated conventionally at S,visible colors of the spectrum can be predetermined. Analysis ofatmospheric conditions may be facilitated. The spacing of the spectrumcolors with relation to the spacing between the opening Hl and rality ofspectroscopic circular coaxial grating i zones on the same plane, andspaced apart predetermined distances and the lines of each zone havingpredetermined spacing relationships to the line spacing of anothergrating zone.

3. A transparent body having a planular surv face, a plurality of spacedapart concentric circular zones of diiraction lines on said surface,

the lines comprising minutely spaced grooves formed in the surfaceseparated by uncut portions, the spacingl of the lines for each zonebethe grating 4a, may afford accurate light analysis for variouspurposes.

Fig. 15 shows grating zones on the opposite sides of a parallelled sidedblock and the light effects from a given source assume very definitecontrasts as a result of change of distance from the light of thegratings affording means of measuring distance or small angledifferences. y

Fig. 16 shows the use of a half disc preferably with lines so spacedthat a spectrum will appear in a narrow band shown in darker lines andby which a sharp angle reading may be made, for example: the changeincolor of a single light out of the line of vision of a driver in avehicle` will appear in the form of a darkened band when seen through awindow or windshield.

We do not wish to limit the scope of our present invention to theillustrative forms, scientific and decorative uses and effects describedand shown except as properly distinguished from prior gratings and asdefined in the appended claims.

We claim:

1. A transparent spectroscope grating having separated coaxial circularzones of grating lines of predetermined spacing and a relation to eachother and uniformly spaced in each zone, Whereby diiracted light raysthrough one may pass through the other and be observed at a commonpoint.

2. A transparent body having thereon a pluing uniform throughout thezone, the spacing of the lines of one zone having a predeterminedrelation to the spacing of the lines of adjacent zones, and thespacingresulting in diffracting color to a common point on the axis normal tothe plane and concentric with the zone circles.

4. A spectroscope comprising a transparent body having parallel sides,grating lines comprising minute grooves of uniform depth formed in acircular zone on opposite sides and within concentric circular bands,the spacing of lines being such that light diffracted into the body fromone band is again difracted by the second band to a focal point on anaxis concentric with both zones.

FRANK J. KAEHNI. WILLIAM L. KAEHNI.'

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 551,769 Jacobson Dec. 24, 1895FOREIGN PATENTS Number Country Date 501,645 Great Britain Feb. 28, 1939OTHER REFERENCES Physical Optics, by R. W. Wood; 1934 edition; page 253cited.

Light, by Lewis Wright, second edition, published 1892, pages 178 and179 cited.

